1. Field of the Invention
The present invention relates to a container transport system and a measurement container for replacing an inside of a container used for a clean room with a gas atmosphere and transporting the container.
2. Description of Related Art
For example, a semiconductor element is manufactured in a clean room whose inside atmosphere is cleaned. At the time of transporting a semiconductor substrate for forming the element between processes, a cassette in which the semiconductor substrate is stored is stored in a transportable sealed container in order to prevent dust from attaching to the semiconductor substrate. The inside atmosphere of the sealed container is replaced with an inert gas such as a nitrogen gas in order to prevent the growth of an oxide film caused due to natural oxidation of the semiconductor substrate.
As described above, the cassette is put into the sealed container filled with the nitrogen gas, and the sealed container is transported and stored. However, the nitrogen gas concentration in the sealed container sometimes becomes equal to or smaller than a prescribed value during waiting for the transport and during storage. In this case, the sealed container with the reduced nitrogen gas concentration is transported to a gas supplying device provided in the clean room to be purged again. Then, the sealed container is returned to the original place.
In Patent Reference-1, as a gas supplying system of this kind, there is proposed a system including a transportable sealed container for storing a semiconductor wafer and a gas supplying device for supplying/discharging the gas. Two gas passage pipes for making inside and outside communicate with each other are formed in the transportable sealed container. The gas supplying device includes a gas supplying passage airtightly communicating with the one gas passage pipe and a gas exhaust passage airtightly communicating with the other gas passage pipe. The gas supplying passage communicates with a gas supplying source for supplying the gas. The gas exhaust passage communicates with a processing device for discharging the gas. In this gas supplying system, the gas is supplied to the transportable sealed container from the gas supplying source via the gas supplying passage and the gas passage pipe. In addition, when the sealed container is filled with the nitrogen gas and the pressure in the sealed container becomes equal to or larger than a predetermined pressure, the gas is discharged to the processing device via the gas exhaust pipe and the gas exhaust passage.
Recently, it becomes general that the plural gas supplying devices of this kind are provided and the flow amount of gas supplied from the gas supplying source is controlled in each of the plural gas supplying devices.
Patent Reference-1: Japanese Patent Application Laid-open under No. 8-203993 (FIG. 1)
In the gas supplying device, the desired flow amount of gas cannot be sometimes supplied due to malfunction of a control circuit in the device and clogging of the gas supplying passage. Therefore, there is proposed a measurement of the gas flow amount by arranging a flow meter in the gas supplying passage of each gas supplying device in order to confirm whether or not the gas flow amount is appropriately supplied.
However, if the flow meter is arranged in each of the gas supplying passage of the gas supplying device, the plural flow meters become necessary. Thus, the cost becomes high. In addition, a space for arranging the flow meter becomes necessary in the gas supplying device.